Typically a Golden has reached it height by the age of 11 months. However they will still fill out up to the age of 18 months. This applies more so for boys than girls. The girls tend to fill out completely around 14 months.

Maturity wise is a different story! You can expect your boy to be immature until he is around 3. Some get mature emotionally faster but that is the typical norm.

Your Golden is almost as big as my brothers. He is about 110 pounds and not an inch of fat on him. He is just a big boy. The breeder said they bred him to be a big dog. Definitely not the breed standard.

Is he neutered? This will help him in his maturity but will do nothing for his height.